I do most of my 3D modelling in Blender - which is open source and has really evolved into a quality tool. It took me a good 2 years of running at blender to get comfortable with it and I'm probably still only using 20% of its functionality for the most part.

I've had a ZBrush license since 2007. I bought it for 70% off on a black Friday sale. Their license is perpetual so you get free software updates for as long as they are around. It's an amazing tool and I've barely scraped the surface of what it can do. I originally bought it for painting skins (it was one of the first with projection painting abilities back int he day) but I find niche places for it in my workflow on a regular basis.

This is a ZBrush add-on tool by Micheal Dunnam, he creates custom brushes for ZBrush and sells a one-time-payment lifetime subscription to his toolset (which is really quite useful). The ruins in my Deep Waters gamejam entry were from the IMM (Insert Multi-Mesh) Ruins brush set.

I use this primarily to bake normal/displacement/ambient occlusion/projected base texture maps from a very high polygonal mesh into a lowpoly one. Comes in handy when working between Blender and ZBrush.

This is a cloth simulation application that uses a pattern based approach (you draw 2D panels and match the seams and it auto-magically sews itself together - you can export the mesh when you're done for rigging in your preferred application. I've studied fashion design / pattern making though continuing education night classes a few years back so I come in with a clear understanding of how clothing fits on a human (avatar) and enjoy the process. I actually don't have a license for this presently but plan on renewing my subscription once I have some time to dedicate to playing with it.